This invention relates to a current probe of the type used for remotely detecting electrical current flowing through a conductor which may, for example, form part of a wiring loom of an automobile.
One conventional type of current probe utilises the Hall-effect and is disclosed in U.K. patent No. 2099159B. The probe has a body portion adapted to be gripped by the hand of an operator and at one end of the body portion is hingeably mounted a pair of jaws which together define a ring of magnetisable material. The jaws are movable between an open position in which they can be placed over an electrical conductor and a closed position in which the jaws meet around a conductor and the ring is substantially complete. Whilst this type of probe is perfectly satisfactory for measuring current flowing in an electrical conductor which is readily accessible, it will be appreciated that where the electrical conductor is disposed in a confined space or is amongst several other conductors, it can be difficult, if not impossible, to attach the probe satisfactorily since the opened jaws of the probe can become snagged.
A further problem arises where the electrical conductor is in such a position that in order to take a satisfactory measurement, the conductor must be pulled towards the operator. With a probe having hinged jaws this can lead to slippage and although this can be overcome to some extent by e.g. incorporating a strong spring within the probe to permanently bias the jaws into a closed position, nevertheless it will be appreciated that this arrangement is far from satisfactory since it then makes the jaws difficult to open unless a mechanical advantage is incorporated into the trigger mechanism.
The above problems are overcome to a limited extent by another probe known in the art which has, instead of hinged jaws, an arrangement in which a rectangular ring of magnetisable material is mounted on the end of a handle-shaped body. One side of the ring is split from the remaining three sides and is slidable within the handle of the probe to thereby permit access into the ring of a conductor. The slidable side of the ring is urged back to a position in which the ring is complete by means of a compression spring held within the handle.
One problem with this second kind of probe known in the art is that the biassing spring acts only along the line of sliding movement because the line of the split is parallel to the line of sliding movement. This in turn means that when the ring is complete additional spring means must be provided to ensure that a good contact is made between the sliding part of the ring and the fixed part. Another disadvantage results from the rectangular shape of the ring of magnetisable material, which shape tends to introduce into the probe signal errors as a result of the consequential assymetry in the magnetic circuit which, ideally, should be generally circular. The rectangular configuration has a further disadvantage, particularly in a Hall-effect proble, in that it is generally not as easy to manufacture as a circular ring, since, if used, the windings that make up the rectangular ring must have a discontinuity at each respective corner of the ring. A still further disadvantage is that unwanted space is taken up by the presence of the sliding part of the ring and the presence of the spring means biassing the sliding part of the ring into good contact with the remaining part of the ring. The problem is not as severe as with a probe of the type in which the jaws are hingeable, but on the other hand the problem is not negligible either.
It is an object of the present invention to provide a current probe in which te aforementioned disadvantages are obviated, the probe being of itself a significant improvement in the art.